Method of making a filter for tobacco smoke



Get. 9, 1956 H. w. KNUDSON 2,765,515

METHOD OF MAKING A FILTER F OR TOBACCO SMOKE Filed Oct. 7, 1953 HAROLD MKNUDSO/V METHOD OF MAKING A FILTER FOR TOBACCO SMOKE Harold W. Knudson,Norwood, Mass., assignor to H & V

Specialties Co., Inc., East Walpole, Mass, at corporation ofMassachusetts, and P. Lorillard Oompany, New York, N. Y., a corporationof New Jersey, jointly Application October 7, 1953, Serial No. 384,673Claims. (CI. 28-72) This invention relates to the treating orconditioning of tobacco smoke to render it less irritating and lesstoxic, and pertains more specifically to a filter for removing aselected portion of the smoke particles in fresh tobacco smoke and to amethod of making the same.

It appears to be generally agreed that tobacco smoke, particularly wheninhaled, is at least potentially harmful, producing undesirablephysiological effects, especially in the case of individuals sufferingfrom cardio-vascular disorders, stomach disorders, and the like; and ithas been found that even apparently physically sound individuals mayshow minor blood pressure changes caused by smoking, although in thecase of such individuals, irritation of the membranes of the nose andthroat is the primary symptom. Despite the potentially harmful effectsof smoking on certain individuals, it has been found that substantialreduction or complete cessation of smoking frequently produces even moreharmful effects because of shock, both physical and psychological, tothe individuals system. This problem is of ever increasing magnitudebecause of the increasing popularity of cigarette smoking.

It has been found that the smoke particles present in fresh tobaccosmoke have for the most part diameters of the order of 0.1 to 0.6 micronand that particles of this size, when inhaled into the lungs, are to alarge extent readily exhaled again. However, particles of these smalldiameters tend to agglomerate into larger particles quite rapidly, evenduring passage through the body of the cigarette, the rate and extent ofagglomeration increasing with the mass concentration of the smokeparticles in 'a given volume of gas or air. A substantial proportion ofsuch small particles, in the mass concentration ordinarily present inthe mouth of an individual smoking an ordinary cigarette, willagglomerate or condense to larger particles having diameters greaterthan 0.6 micron in a period of time of the order of a few microseconds.These large particles which are formed in the month before the smoke isinhaled into the lungs may to some extent be condensed upon the tongueand the membranes of the nose and throat by impingement thereagainst,but many survive to be drawn into the lungs, where a substantialproportion are retained by impingement upon the tissues.

Furthermore, when the mass concentration of the smoke particles is high,as is normally the case in smoking ordinary cigarettes, agglomerationand condensation of the small smoke particles continue as theseparticles are inhaled, larger smoke particles being formed during theperiod while the smoke is in the trachea, bronchi, and lungs. The largeparticles thus formed are not completely removed by exhalation but tendto impinge against and be condensed on the tissue of the lungs, bronchi,and trachea. It is the large particles, retained in the lungs, which arebelieved to be primarily responsible for undesirable physiologicalchanges.

Elimination of all of the smoke particles is undesirable, since thatleaves only a colorless and highly unpalatable mixture of combustiongases. However, it has of the smoke particle been found that the presentinvention is capable of removing not only the large agglomerated smokeparticles, but also a substantial proportion of the small particlespresent in tobacco smoke as it is drawn into the mouth, thus resultingin a greatly reduced mass concentration of smoke particles in the smokewhich is inhaled, and greatly reducing the rate of agglomeration orcondensation of these particles with each other to form larger smokeparticles in situ. As a result, the undesirable physio logicalconsequences of the accumulation of smoke particles in the lungs andrespiratory tract are substantially avoided.

The invention will be described with reference to certain embodimentsshown in the appended drawings in which:

Fig. 1 is a schematic representation of the path of a smoke particlepast a fiber of large diameter, such as the fibers present in tobaccosmoke filters of the prior art;

Fig. 1a is a similar representation of the path of a smoke particle pasta fiber of small diameter;

Fig. 2 is a view in elevation, partly broken away and in section, of afilter of the present invention embodied in a cigarette;

Fig. 3 is an end elevation of another embodiment of my invention;

Fig. 4 is a view in elevation, partly broken away and in section, of asmoking pipe embodying the present invention; and

Fig. 5 is a view in elevation, partly broken away and in section, of acigarette holder embodying the present invention.

As was pointed out above, smoke drawn into the mouth from an ordinarycigarette contains a predominant proportion of particles of about 0.1 to0.6 micron diameter. Since the diameter of ordinary paper fibers ortextile fibers of the type heretofore employed in tobacco filters is ofthe order of 10.0 to 25.0 microns, there is present, in the case of thesmall particles, a situation such as portrayed in Fig. 1 where A is asmoke particle, B is a cross-sectional view of the fiber, C is a slipline representing the flow of the air or gas stream past the fiber, andD is a similar slip line with the Brownian movement of theparticle(denoted by the wavy line F) superimposed thereon. In order for thesmoke particle to be removed from the air or gas stream, it must impingeagainst or collide with the fiber. The possibility of such collision orimpingement in the case of such large diameter fibers are remote,because distortion of the slip line around the fiber is sufii-cientlygreat to overcome the effect of inertia as well as the effect ofdisplacement due to the Brownian movement.

I have found that by employing in such a filter obstructions having adiameter of the order of the diameter of the smoke particles to beremoved, that is, having a diameter of the order of 0.1 to 2.0 microns,the smoke particles A do readily impinge against the obstructionindicated by B in Fig. la. The reason for this impingement apparently isthat the distortion of theslip stream C around the small diameterobstruction B is not sufficiently great to overcome the inertia of theparticle and not greater than the magnitude of'the Brownian movement, asindicated by F, although I do not wish to be bound by this theory. Inthe case of the large diameter obstruction B of Fig. I, obviously a muchhigher velocity than is realized with cigarettes in practice would berequired to achieve this result.

Accordingly, the filtering medium of the present invention takes theform of a screening or filter member disposed in the path of the tobaccosmoke in the form of a stereoreticulate mass including obstructions,such as fibers having for the most part a diameter of 0.1 to 2.0

microns, approaching the diameters of the smoke particles to be removed,theseobstructions being interdispersed and mixed with obstructions, suchas fibers, of substantially larger diameter.

The small diameter obstructions prefefably' take the form of fibers.Mineral fibers, suchas asbestos; or glass fibers of the specifieddiameters have been foundto be particularly satisfactory. However,fibers of a variety of other materials, such as nylon, celluloseacetate, viscose rayon, and polyester fibers; such as Orl'on' andDacron, are satisfactory provided their diameters are within thespecified range.

The obstructions of larger diameter also preferably take the form offibers, conventional textile fibers, such as cotton, rayon, orother'cellu'losic fibers being preferred. Wool and nylon fibers, as wellas fibers of other synthetic textile materials, may also be employed.These fibers normally have diameters of an order of 10.0 to 25.0microns.

The length of the small diameter fibers or obstructions present in thefilter is very small. Opening of asbestos to the extent required toprovide fibers of the desired range of diameter inherently results inbreaking of the fibers so that they range in length from 0.1 to a'maximum of 3.0 mm. Even when the asbestos is thoroughly opened, theremay remain occasional bundles or' sticks of large diameter (over 2.0microns) ranging in length up toabout 6 mm. However, all of the smalldiameter fibers (0.1- 2.0 microns) will be no more than 3 mm. in length,and the major proportion will be very much shorter-of the order of 0.1to 0.3 mm. 1

The length of the larger diameter fibers or obstructions is not criticaland may vary upwardly from 3 inch or even less, although they preferablyare at least A inch in length and may be of greater lengths up toseveral inches, although normally such fibers will be no longer than theoverall dimensions of the filter.

In order to reduce themass concentration of the smoke particlessufiiciently to have the desired eifec't upon the rate ofagglomerationof these particles, and hence upon the extent of retentionof smoke particles in the mouth and nose, and particularly in the lungsof the smoker, while at the same time avoiding objectionable impairmentof the odor and flavor of the tobacco, it has been found thatapproximately 40% to 60%" by weight of the smoke particles shouldpreferably be removed from the smoke. Accordingly, the preferredembodiment of the invention is a' filter designed to remove 40% to 60%by weight of the tars and nicotine which form the smoke particles. Inorder' to achieve this preferred result, the filter should include from10% to 30% by weight of small diameter obstructions or fibers", thebalance being fibers or obstructions of larger diameter.

it will of course be understood that the quantity of the tobacco smokeparticles removed is not entirely afunction of the relative weights" ofthe small diameter and large diameter fibers since the density orcompactness of the mixed fibers and the overall dimensions of the filteralso affect the result. In order to achieve the desired result withcigarettes, a filter which includes from 10% to 30% by weight of smalldiameter fibers preferably has a diameter from 0.81 to 0.83 centimeter,a length from 1.0 to 1.2 centimeter, and an apparent specific gravity(weight per unit volume) from 0.1 to 0.23 gram per'cubic centimeter, theratio of solids to voids by volume being of the order of 1:10 to 1:30,usually about 1:25. It has been found that a filter having thesedimensions and the specified apparent specific gravity is capable ofremoving the desired proportion of smoke particles without objectionablereduction or impairment of the draw or case with which the smoke isdrawn through the filter.

In the manufacture of my filter, it is important that the blending ofthe two classes of fibers be as uniform as possible. In addition, it isimportant that the small diameter fibers be thoroughly opened, thedegree of opening required being much greater than is the case withasbestos fibers which have been commercially available heretofore. Theopening of such fibers, which normally contain substantial quantities ofsticks (fiber clusters or agglomerates), may be accomplished by acrushing and grinding operation, as on a hammer mill, followed byscreening and further opening of the fibers on a mixing picker andcarding machine while simultaneously blending the opened fibers with atleast a portion of the larger diameter fibers. If the opening. of thesmall diameter fibers is carried out in the absence of the largerfibers, it has been found that they tend to reagglomer'ate into clustersbefore they can be interdispersed or blended with the larger diameterfibers. If the small diameter fibers are blended with the total amountof large diam eter fibers in one operation,v the resulting fiber mass isso large and flufiy, due to the extreme mechanical action necessary tocompletely open the small fibers, that it cannot be accommodated onsuitable processing machinery. Best results have been obtained by firstblending the small diameter fibers with approximately an equal weight oflarger diameter fibers, the remainder of the larger diameter fibersbeing interdispersed in the mixture in a second step. For example, thesmall diameter fibers and an equal weight of the larger diameter fibersmay be fed together to the mixing picker where they are opened andblended. This blend is then fed with the remaining portion of the largefibers through a second mixing picker for further opening and blending.This blended mass is fed into a breaker carding machine, thence into afinishing carding machine from which it is obtained in the form of a webor roving. Alternatively a mixing picker such as is used in the woolindustry may be employed for the formation of a lap of mixed fibers andthe lap may be delivered to the feed apron of a wool carding machine.

The two fibers in the desired proportions may also be fed into a hardwaste opener which comprises a drum and pins picking from two sets offeed rollers and which provides extreme retting of the fibers. The blendof small diameter fibers with a portion of the large diameter fibersthus prepared is then fed to a mixing picker or to a wool mixing pickertogether with the balance of the large diameter fibers, and from thereto a carding machine.

It has also been found that air-laid webs of the fibers mixture, such asthose which are formed on a Rando- Webber machine by feeding the openedand blended fibers into an air blast which then deposits them as a webupon a rotating perforated cylindrical condenser are eminentlysatisfactory for the purpose of the present invention.

The larger diameter fibers in the fiber mixture serve to maintain thestructure sufficiently open to permit ready passage of air and toprevent excessive impairment of draw. In the absence of such largediameter fibers, the density of the filter would be such that it wouldbe virtually impossible to draw smoke through it. In the preferred formof the invention, the resistance of the filter to draw is notsubstantially greater than an equivalent volume of tobacco as containedin a cigar, cigarette, or pipe, the filter under these conditionseffectively removing from 40% to 60% by weight of the tars and nicotine,i. e., of the smoke particles.

However, it should be understood that the range of proportions of smalldiameter and large diameter fibers is not critical. Even with amounts ofsmall diameter fibers as low as 1% by weight of the mixture, the filterof the present invention shows a distinct improvement over the crepepaper or all cotton filters of the prior art. Normally, however, thefilters of the present invention should contain at least 5% by weight ofsmall diameter fibers and in some cases it may be desirable to increasethe proportion of small diameter fibers to as much as 30% by weight ormore despite the fact that at this point there is definite impairment oftaste and flavor of the smoke.

The web of mixed fibers prepared as described above may be formed into afilter in several ways. In some cases I have found it desirable to applya hinder or bonding material to the fiber mixture in order to bindtogether the individual fibers or a substantial proportion of them attheir intersections to render the filter firm and resilient and toprevent undue compression with consequent impairment of draw. The bindermaterial may be a thermoplastic or thermo-sensitive material if desired,such as a synthetic resinous binder. Among the resins which may beemployed are polyethylene, polystyrene, polymers and copolymers of vinylchloride, vinyl acetate, vinylidene chloride, methyl acrylate, methylmethacrylate, and the like, polyvinyl acetals such as polyvinyl butyral,polyester resins phenol formaldehyde, and the like. Preferably thethermo-sensitive binders have a softening point or activation pointbetween about 150 and 300 F. The binder material may be applied to thefiber mixture in the form of particles of dry solid material or liquidsdroplets, or a dispersion or emulsion of the binder material in anaqueous or other liquid medium may also be employed. In any event, thebinder material may be applied to the fiber mixture by blowing orspraying or by any other suitable means. If the bonding material isapplied to the fibers in the form of a solution, care should be taken tocoat only the larger diameter fibers, as for example by coating suchfibers before they are blended with the fibers of small diameter.

If desired, the binder material itself may take the form of a fibrousmaterial, and may replace a part or all of either the small diameter orthe large diameter fibers in the fibrous mixture. In such cases, thefibrous binder material is preferably thermo-sensitive so that asubsequent heating step is required to activate the binder material andcause the fibers to be bonded together at their intersections. It hasalso been found that the binder material may be applied as a coating onat least a portion of the large diameter fibers, this coating, when thebinder material is thermo-sensitive, being activated by a subsequentheating step.

When the binder material is applied to the fiber mixture, care should betaken to avoid providing a continuous coating of binder material for anysubstantial proportion of the small diameter fibers, since such acoating will tend to increase the diameter of these fibers beyond theeffective range. The proportion of binder material to fiber mixture isabout 10% to 25% by weight, preferably about 15% by weight.

The web of mixed fibers, which may be of any desired thickness rangingfrom a few hundredths of an inch upwards, may be formed into a filterunit by several different methods. In one embodiment of the invention,an approximately cylindrical rod shaped roving may be rawn from the weband cut into the lengths desired for the particular filter. In order toachieve the desired apparent density in the finished filter, the rovingmay be compressed radially as by passing it through a suitable tubulardie, the extent of compression depending, of course, upon the initialapparent density of the roving. Normally, the diameter of the compressedroving is from one-half to one-tenth that of the uncompressed roving. Ifdesired, the initial roving may be of relatively small diameter and twoor more such rovings may be combined with a light twist. In any event,the small diameter fibers are arranged in random or heterogeneousfashion in the finished filter, but the larger diameter fibers, asubstantial proportion of which are oriented longitudinally of the webby the carding operation, are still further oriented when the roving isdrawn from the web, so that in the roving the major proportion of thelarger diameter fibers extend generally longitudinally of the roving.When a binder material is employed, the binder may suffice to maintainthe roving in the desired state of compression either by applying thebinder material to the roving while it is maintained in a compressedcondition or by activating a previously applied thermo-sensitive binderby heating during this period.

' A textile fabric, either finely woven or of open mesh,

may also be employed, particularly in the case of a filter for a pipe orcigarette holder. Encasement of the roving in the wrapping material maybe accomplished by depositing the roving upon an elongated strip of thewrapping material bent into approximately U-shape in transverse section,then passing the assembly through a tubular die so as to compress theroving and simultaneously lap the edges of the wrapping material, whichmay be bonded together by any suitable means, such as a conventionalcigarette paper adhesive applied in a conventional manner. When awrapping is employed, activation of the thermo-sensitive binder, ifpresent, may be brought about by heating after the wrapping is applied.Any suitable heating means may be employed, followed if necessary by acooling step. Following encasement of the roving in the wrapping, theresulting elongated cylinder may be severed transversely into lengthsdesired for the individual filter units.

As shown in Fig. 2 of the drawing, the individual filter element 10consisting of a roving including Bolivian blue asbestos fibers andcotton fibers is encased within a wrapping 12 which may simulate ivoryor cork, for example, to provide a conventional tip on cigarette 14.

In Figs. 4 and 5, a similar roving 10 having somewhat different overalldimensions and encased within suitable wrappings 18 and 20,respectively, is shown as employed for filtering smoke in a pipe or acigarette holder. Because of the greater efficiency of the filters, theybecome loaded with tars and nicotine much sooner than conventionalfilters and accordingly should be changed more often. However, thefilter of Fig. 5, for example, even after the smoking of say tencigarettes, is still upwards of 200% more efficient than a conventionalcrepe paper or spun viscose filter freshly inserted in the holder.

Additional mechanical strength may be imparted to the roving whennecessary or desirable by braiding the roving with another elongatedfibrous material, such as cotton thread or yarn or any other suitabletextile yarn or thread, following which the braided roving may beencased in a suitable wrapping if desired as described above.

In another embodiment of the invention, the web of mixed fibers may alsobe formed into a suitable individual filter element by interleaving theweb with layers of a denser paper-like material to form the filterillustrated in Fig. 3 wherein the Web of mixed fibers 10 is folded orspirally wrapped along with crepe paper 16, the whole being compressedwithin an encasing wrapping material 12, such as paper. The efiiciencyof such a filter is at least 500% as great as the efliciency of the samestructure without the web of fibrous material, assuming a weight ratioas between the fibrous web (comprising 10% to 20% asbestos fibers) andthe crepe paper of approximately 1:2.

In forming such an interleaved filter construction, one or more layersof fibrous web may be plied up with one or more layers of crepe paper orthe like to form a laminate, and the laminate may be folded or rolledupon itself into an elongated generally cylindrical form which is thenencased in the same wrapping as may be employed for the roving. A bindermaterial for the fibers of the web may be employed in this case also andthe laminate may be compressed to any desired extent during or after itsformation into a cylinder, as by passing the generally cylindricalassembly through a tubular die while encasing it within the wrapping.Following the wrapping, the assembly may be severed transversely intoany desired lengths to form the individual filter units.

This application is a continuation in part of my copending applicationSerial No. 260,187 filed December 6, 1951.

Although I have herein described specific embodiments of my invention, Ido not intend to limit myself solely thereto, but to include all of theobvious variations and modifications within the spirit and scope of theappended claims.

I claim:

1. The method of making a tobacco smoke filter which comprises openingand blending fibers having a diameter of the order of 0.1 to 2.0 micronsand fibers of larger diameter, interdispersing said blend withadditional hers of said larger diameter to form a web in which theweight of said larger diameter fibers amounts to from 70% to 95% of thetotal weight of fibers, and compressing said web within a tubularwrapping to an apparent density from 0.1 to 0.23 gram per cubiccentimeter.

2. The method of making a tobacco smoke filter which comprises openingand blending a mass of fibers having diameters of the order of 0.1 to2.0 microns with a mass of fibers of larger diameter, interdispersingsaid blend with additional fibers of said larger diameter to form a web,forming said web into a roving, encasing the roving in a substantiallyimpervious wrapping, and severing the encased roving transversely intoindividual filter elements.

3. The method of making a tobacco smoke filter which comprises openingand blending a mass of fibers having diameters of the order of 0.1 to2.0 microns with a mass of fibers of larger diameter, interdispersingsaid blend with additional fibers of said larger diameter to form a web,interleaving said web with layers of paper to form a laminate,compressing said laminate into tubular form and encasing it in asubstantially impervious wrapping, and severing the encased laminatetransversely into individual filter elements.

4. The method as defined in claim 9 wherein at least some of the fibersare thermo-sensitive and including the step of heating the fiber mixtureto bond said thermosensitive fibers to other fibers at theirintersections.

5. The method of making a tobacco smoke filter which comprises openingand mixing fibers having a diameter of the order of 0.1 to 2.0 micronsand fibers of larger diameter, forming the fiber mixture into a web,forming the web into a roving, braiding the roving with anotherelongated mass of fibrous material to add strength thereto, encasing thebraided roving in a substantially impervious wrapping, and severing theencased braided roving transversely into individual filter elements.

6. The method of making a tobacco smoke filter which comprises openingand blending a mass of fibers having diameters of the order of 0.1 to2.0 microns with a mass of fibers of larger diameter, lnterdispersingsaid blend with additional fibers of said larger diameter to form a web,applying to said fiber mixture a bonding material adapted to bond thefibers together at their intersections, encasing said fiber mixture in asubstantially impervious tubular wrapping, and severing said encasedfibers into individual filter units.

7. The method of claim 6 wherein the bonding material isthermo-sensitive and the fiber mixture is heated after application ofthe bonding material thereto to activate the bonding material and tobond at least some of the fibers together at their intersections.

8. The method of making a tobacco smoke filter which comprises openingand mixing fibers having a diameter of the order of 0.1 to 2.0 micronsand fibers of larger diameter. forming the fiber mixture into a web,forming the web into a roving, braiding the roving with anotherelongated mass of fibrous material to add strength thereto, and severingthe braided roving transversely into individual filter elements.

9. The method as defined in claim 8 wherein at least some of the largerdiameter fibers are thermosensitive and including the step of heatingthe fiber mixture to bond said thermosensitive fibers to other fibers attheir intersections.

10. The method of making a tobacco smoke filter which comprises openingand blending a mass of fibers having diameters of the order of 0.1 to2.0 microns with a mass of fibers of larger diameter, interdispersingsaid blend with additional fibers of said larger diameter to form a web,forming said web into a roving, braiding the roving with anotherelongated mass of fibrous material to add strength thereto, and severingthe braided roving transversely into individual filter elements.

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